You need access to a command line shell, via the console application, or telnet or putty if it's a remote machine. Then you will need to do something like:

cd /home/httpd/vhosts/knowittv.com
ls -ld /home/httpd/mason

This will show you what permissions are currently set for the directory, you should see something like:

drwxr-xr-x 2 simon www-data 4096 2010-01-08 12:58 mason

This tells you that "simon" is the owner of the file (probably this will be your username), and that it also belongs to members of the group "www-data" - this should be the group that apache is running in. Depending on the apache set-up, it might be "www-data" or it might be "nobody", or anything else.
So, the letters at the beginning tell you "d" - the file is a directory, "rwx" - the owner simon, has all permissions, "r-x" - the group has only read and execute permissions, and "r-x" again - everybody else also has only read and execute. Thus, apache cannot write to this directory.
To give write permission to the group, enter

chmod g+w mason

Don't worry if your file doesn't exactly match these parameters, the important thing is to make sure that the group includes the apache processes, and that the group has write permission.

It could be that you yourself are denied permission to the file, in which case you will have to become the superuser, or root.